You're being exposed to radiation -- but it's the amount that counts

Everyone gets some radiation from a variety of sources like these. It's the level of exposure that matters to your health.

CT scans are among the sources of radiation to which people might be exposed. (Stefano Paltera / For The…)

Everyone is exposed to some radiation. It's the level of exposure that determines whether there's any harmful effect.

But how much radiation is a lot? Here are a few numbers for comparison.

(A microsievert is a unit that measures the biological effects of radiation.)

Limit on whole-body exposure for a radiation worker for one year: 50,000 microsieverts

One year's worth of exposure to natural radiation from soil, cosmic rays and other sources: 3,000 microsieverts

One chest X-ray: 100 microsieverts

One dental X-ray: 40-150 microsieverts

One mammogram: 700 microsieverts

CT scan (abdomen): 8,000 microsieverts

Full-body airport X-ray scanner: 0.0148 microsieverts

Airplane flight from New York to Los Angeles: 30-40 microsieverts

Smoking a pack a day for one year: 80,000 microsieverts

Average dose to people living within 10 miles of 1979 Three Mile Island accident: 80 microsieverts

Average radiation dose to evacuees from areas highly contaminated by the Chernobyl disaster: 33,000 microsieverts (Of 600,000 of the most-affected people, cancer risk went up by a few percentage points -- perhaps eventually representing an extra 4,000 fatal cancers on top of the 100,000 fatal cancers otherwise expected.)